1. Technical Field of the Invention
The present invention relates generally to an easy-to-assemble structure of an electric power steering device which may be employed to assist in turning a steering wheel of automotive vehicles.
2. Background Art
Typical electric power steering devices include an assemble of a torque sensor working to measure a steering torque added to a steering wheel, a controller working to determine a steering assist torque as a function of the measured steering torque, an electric motor outputting the steering assist torque as determined by the controller, and a torque transmission mechanism working to transmit the output of the electric motor to wheels to be steered. The controller has a substrate on which a switching transistor working to control a duty cycle of current flowing through the electric motor and electrical parts are fabricated. The switching transistor is not mounted directly on the substrate because of heat generated therefrom, and retained by a housing within which the torque transmission mechanism is installed. The switching transistor is soldered to the substrate. For instance, Japanese Patent First Publication No. 8-188164 discloses such a structure.
The above structure, however, has a drawback in that an assembling process of soldering the switching transistor to the substrate of the controller is separate from that of installing the torque transmission mechanism within the housing, thus resulting in a difficulty in joining the switching transistor to the substrate of the controller.